|KIM, DO HYUNG - University Of Kentucky|
|MCLEOD, KYLE - University Of Kentucky|
|KOONTZ, ANNE - University Of Kentucky|
|FOOTE, ANDREW - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
Submitted to: Animal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2014
Publication Date: 1/1/2015
Citation: Kim, D., McLeod, K.R., Koontz, A.F., Foote, A.P., Klotz, J.L., Harmon, D.L. 2015. Effect of intake on fasting heat production, respiratory quotient and plasma metabolites measured using the washed rumen technique. Animal. 9:58-66.
Interpretive Summary: The objective was to investigate the effect of intake prior to fasting on concentrations of metabolites and hormones RQ and HP using the washed rumen technique and to compare these values with those from the fed state. Measurement of maintenance energy requirements in cattle uses estimates of fasting heat production made during the third and fourth day of fasting, when a respiratory quotient has fallen to approximately 0.7. However, this approach can cause stress and produces a severe energy deficit caused by the extended fasting period required. As an alternative to traditional fasting methodologies, a washed rumen technique indicates that heat production no longer reflects the continuing metabolism of the diet and a respiratory quotient decreases to 0.7, minimizing the time required as opposed to traditional fasting methodologies, without causing a severe energy deficit and stress. In most previous studies, cattle adapted by restricted nutrition around maintenance for 3- to 6-week prior to fasting, after then fasting HP normally measured for 4-day. However, this approach might lead to an underestimate of fasting HP because prolonged fasting duration can decrease the basal metabolic rate and induces ketosis above thresholds. As an alternative to traditional fasting methodologies, fasting state achieved using a washed rumen technique indicates that heat production no longer reflects the continuing metabolism of the diet, which are the disappearance of CH4 production and a decrease of respiratory quotient to 0.7. Also, the washed rumen technique reflects the nutritional status provided prior to fasting, which provides a consistent response. Therefore, application of the washed rumen technique for estimation of fasting heat production produces a rapid and relatively stable period for estimation of heat production that is indicative of mild nutrient restriction and minimal stress. A short-duration of fasting using the washed rumen technique may provide an alternative to traditional fasting methodologies, and may be more representative of the producing animal, without a severe energy deficit and stress associated with long-term fasting.
Technical Abstract: The objective was to investigate the effect of intake prior to fasting on concentrations of metabolites and hormones, respiratory quotient (RQ) and fasting heat production (HP) using the washed rumen technique and to compare these values with those from the fed state. Six Holstein steers (360 ± 22 kg) were maintained at 21°C and fed 3 different energy intakes within a replicated 3 × 3 Latin square design with 21-day periods. Steers were fed alfalfa cubes to provide 1.0, 1.5, and 2.0 × NEm during 19 days of each experimental period. Steers were placed in individual metabolism stalls fitted with indirect calorimetry head-boxes on day 20 of each experimental period (FED steers) and fed their normal meal. On day 21 of each period the reticulorumen was emptied, washed and refilled with ruminal buffer (NaCl = 96; NaHCO3 = 24; KHCO3 = 30; K2HPO4 = 2; CaCl2 = 1.5; MgCl2 = 1.5 mmol/kg of buffer) aerated with 75% N2 and 25% CO2 before introduction to the rumen (steers were not fed; WASHED steers). Each gas exchange was measured over 24 h. Heat production for 1.0, 1.5, and 2.0 × NEm were 479, 597, and 714 kJ/(d·kg0.75) (SEM = 16), respectively. The plateau RQ was 0.756, 0.824, and 0.860 for the 1.0, 1.5, and 2.0 × NEm intakes for the FED steers, respectively. After rumen washing, fasting HP was 331, 359, and 400 kJ/(d·kg0.75) (SEM = 13) for 1.0, 1.5, and 2.0 × NEm intakes prior to fasting, respectively. The RQ for Washed rumen steers was 0.717, 0.710, and 0.719, respectively. Cortisol and ß-hydroxybutyrate concentrations in Washed rumen steers did not exceed threshold levels for severe energy deficit and stress as can be induced from prolonged fasting. This study demonstrates that a fasting state can be emulated using the washed rumen technique, minimizing the time required as opposed to traditional fasting methodologies, without causing a severe energy deficit and stress.